St. Athanasius on the Trinity and Baptism

St. Athanasius the Great ca. 297-373

The faith in the Trinity transmitted to us is the only one, and it unites us with God, and whoever takes something away from the Trinity and baptizes in the name of the Father, or in the Son alone, or into the Father and the Son without the Spirit, receives nothing, but those being baptized and he imagines himself to be giving baptism remain in vanity and unconsecrated, because the Mystery is accomplished in the name of the Trinity: so that whoever seperates the Son from the Father or reduces the Spirit to a creature has neither the Son nor the Father but is an atheist, worse than an unbeliever, and anything but a Christian. (Epistle to Serapion 1.30)